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Fort Jefferson, Powder Magazine A, Garden Key, Key West, Monroe County, FL


Fort Jefferson, Powder Magazine A, Garden Key, Key West, Monroe County, FL



Fort Jefferson was part of Fort Jefferson National Monument from 1935 to 1992. Since then it has been part of Dry Tortugas National Park. The address for the survey has been updated to reflect this change.
This survey originally used the name "Fort Jefferson, Powder Magazine A." Research by staff at Dry Tortugas National Park indicated that name was incorrect, so it was changed to "Fort Jefferson, Large Detached Magazine."
Significance: Located on the Parade Grounds to support the military functioning of Fort Jefferson were the Large and Small detached magazines, where the gun powder was to be safely stored. The large magazine was intended to serve as the main powder storage facility, supplemented by the Small Magazine and lesser magazines occupying two casemates of each long curtain wall and in each bastion tower. The Large Magazine utilized the innovated, shell-proof, barrel-vaulted brick arch and concrete construction for which its designer, Chief Engineer of the U.S. Army General Joseph Totten, was well known. According to the original specifications for Fort Jefferson, there were to be five independent or free-standing magazines two of which were to measure 48' x 28' and three, 30' x 28'. Instead, Large and Small magazines were built, with the former measuring 52' x 71'. Detailed instructions for the construction of the Large Magazine did not arrive at the fort until December 1861, however, following the start during the previous spring of the Civil War, when the fort witnessed its highest use. While Totten instructed work to begin immediately, the Large Magazine was not begun until after the war. In June 1865 it was reported that the foundation was completed. In June of the following year, a small engineering force with the aid of prison labor was able to turn the arch of the large interior magazine, reaching a height of 13'-6". Work continued between 1866 and 1870, although the Large and Small parade magazines were never truly finished. By 1876 they were no longer necessary and by 1891, all the fort's magazines were emptied of powder and munitions. Although structurally sound, the magazines show damage by weaponry fire.
Survey number: HABS FL-44-C
Building/structure dates: 1865-1870 Initial Construction
National Register of Historic Places NRIS Number: 70000069, 01000228



1935 - 1970


Historic American Buildings Survey, creator


Key West (Fla.)24.55506, -81.77999
Google Map of 24.5550593, -81.7799871


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